pgsql: libpq: Fix PQtrace() format for non-printable characters

libpq: Fix PQtrace() format for non-printable characters

PQtrace() was generating its output for non-printable characters without
casting the characters printed with unsigned char, leading to some extra
"\xffffff" generated in the output due to the fact that char may be
signed.

Oversights introduced by commit 198b3716dba6, so backpatch down to v14.

Author: Ran Benita <ran@unusedvar.com>
Discussion: /messages/by-id/a3383211-4539-459b-9d51-95c736ef08e0@app.fastmail.com
Backpatch-through: 14

Branch
------
REL_14_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/0cc540f0d03f280625ea9cda4d43bd79b5f8321d

Modified Files
--------------
src/interfaces/libpq/fe-trace.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)